1. Field of the Invention
This invention generally relates to automotive electrical and control systems, and more specifically to diagnostic testing apparatus for testing the integrity of electrical components and circuits in the automotive field.
2. Prior Art
Automotive electrical systems and microprocessor and other "intelligent" controls therefor have become increasingly complex through recent years. In today's modern car an electrical control module (ECM) constitutes the center of operation and typically is programmed to control the variety of electrical components in the automotive electrical system. The ECM receives input signals or parameters from various sensors and/or switches including vehicle speed, transmission/transaxle gear indication, time, throttle position, park/neutral mode, manifold absolute pressure, system voltage, exhaust oxygen content, engine detonation, engine cranking mode, engine crankshaft position, engine coolant temperature, barometric pressure, and air conditioning system engagement. The ECM continually monitors this input information and produces output commands based on logic analysis to control the operation of various electrical components, which include the idle air control (IAC) motor, sequential fuel injectors (SFI), electric fuel pump, air conditioner compressor clutch, engine cooling fan control, electronic spark timing, air control valve, air switching valve, canister purge control valve, exhaust gas recirculation control, transmission/transaxle torque converter clutch and air door control.
Automotive diagnostic equipment and systems have followed the same trend as electrical systems per se and have become quite sophisticated, complex and expensive. In fact, it is believed that automobile manufacturers traditionally prefer and authorize the use of complex diagnostic equipment that generally can only be afforded by "authorized" factory service departments, particularly since the software programs of such testing equipment are designed for the ECM and electrical systems of that manufacturer's automobiles. Thus, other than conventional ammeter and like continuity testers, there has been no good, inexpensive and universal diagnostic tester available to both skilled and unskilled automotive mechanics for testing the integrity of many electrical components controlled by the electronic control module (ECM) of various automotive systems so that there can be a reliable and simple diagnosis of faults for repair.
It is also known that prior automotive diagnostic equipment has been designed to test different electrical system components normally controlled by the ECM, but such components are generally not tested under actual operating conditions. Instead, the component is usually isolated from the ECM circuitry and the test equipment inputs its own pulse train signals. In other words, the operator may be unable to determine the source or nature of a fault because the ECM is no longer controlling the component. If the ECM is not "live" in the circuit, the test results cannot accurately determine whether the component is receiving proper pulsing signals or is faulty per se.